Simple intro analysis: are downstream DO values within the range of upstream values on any given day? We focus here on the on daily minima and maxima as they reflect GPP and ER, respectively. For example, if the downstream minimum DO on day 1 was 8 mg/L, and the minima for the two upstream sites were 8.5 mg/L and 9 mg/L, then the downstream minimum would be “below” the range constrained by the upstream sites. This would imply non-conservative mixing behavior.

The sites below are arranged from left-to-right by decreasing difference in confluence tributary specific conductance. i.e., the Fontbonne-Violay confluence has the greatest relative specific conductivity difference (145%) and the Coise-Coizet has the smallest relative difference (1%).

We see that for the all sites, less than half of the days with coincident upstream-downstream measurements have the downstream maximum constrained by upstream measurements. This is similar for daily minima.

We can be slightly more quantitative by calculating the relative difference between upstream and downstream values, again focusing on daily maxima and minima. We further focus only on days when the downstream maximum was GREATER than the upstream maxima, and days when the downstream minima was LESS than the upstream minima.

It looks like most differences are in the 5–15% range, but there does appear to be a decreasing trend in a “multiplicative effect” of daily maxima as specific conducivity differences decrease.

Do these differences happen in particular times of the year as opposed to others?

Hard to tell. Below are the two confluences with the greatest SC differences, and you can look at specific dates and times by zooming. It can be be a bit slow to respond because there is so much data, but it will get there after a few seconds.